This invention relates in general to coupling devices for connecting first and second members together for concurrent rotation. In particular, this invention relates to an improved structure for a torsional vibration dampening assembly for use either as a direct coupling between such first and second members or as a driven disc assembly in a clutch for selectively connecting such first and second members.
Rotational coupling devices are structures that are adapted to connect first and second members together for concurrent rotation. For example, in the context of a vehicle drive train system, a rotational coupling device can be used to connect a source of rotational power, such as a flywheel that is secured to an engine driven crankshaft, to a rotatably driven device, such as an input shaft of a transmission. In some instances, the rotational coupling device provides a direct connection between the two members such that the flywheel constantly rotatably drives the input shaft of the transmission. In other instances, the rotational coupling device is provided within a clutch that selectively connects the two members such that the flywheel intermittently rotatably drives the input shaft of the transmission.
In such a vehicle drive train system, it is known that relatively high frequency torsional vibrations can be transmitted from the engine through the rotational coupling device to the transmission and other components of the drive train system. Such torsional vibrations can generate undesirable noise. To prevent or minimize this from occurring, it is often desirable to provide the rotational coupling device with a torsional vibration dampening assembly. The torsional vibration dampening assembly is adapted to reduce the magnitude of torsional vibrations that are transmitted through the rotational coupling device from the flywheel to the input shaft of the transmission.
To accomplish this, a typical torsional vibration dampening assembly includes two rotary torque transmitting elements that are rotatable relative to one another throughout a limited angular distance. The two rotary torque transmitting elements are connected together by a lost motion connection and by a spring damper drive. The lost motion connection is utilized to establish a positive driving connection between the two rotary torque transmitting elements, while permitting a limited range of free movement therebetween. The spring damper drive is utilized to establish a resilient driving connection between the two rotary torque transmitting elements within the limited range of free movement permitted by the lost motion connection. The spring damper drive can also be utilized to tune the vehicle drive train system so as to prevent or minimize vibrations from occurring therein within the operating speed range of the engine.
Although known torsional vibration dampening assemblies have functioned satisfactorily, it has been found that the torsional vibrations from the engine can still be transmitted from the engine to the transmission and other components of the drive train system, generating undesirable noise. Thus, it would be desirable to provide an improved structure for a torsional vibration dampening assembly that provides better vibration isolation and, consequently, reduces the amount of noise that is generated during use.
This invention relates to an improved structure for a torsional vibration dampening assembly for use in a rotational coupling device, such as in a vehicle drive train system. The torsional vibration dampening assembly includes a hub having a radially outwardly extending flange. A plurality of openings are formed through the annular flange. A pair of cover plates are supported on the hub for rotation relative thereto. Each of the cover plates has a plurality of openings formed therethrough that correspond in number and location to the openings formed through the annular flange of the hub. A first stage vibration damper extends between the second cover plate and the hub. The first stage vibration damper includes an annular central damper element having inner and outer rings secured thereto. A second stage vibration damper includes a spring damper assembly that is provided in each of the openings formed through the flange of the hub and the first and second cover plates. Each of the spring damper assemblies includes a resilient member, such a coiled spring, having ends that react against first and second end caps. A movement restraining structure is provided for restraining the end caps from moving freely relative to one another under the urging of the spring. A hollow cylindrical isolation sleeve is disposed about the spring and extends axially between the end caps. The isolation sleeve prevents the spring from directly engaging the sides of the openings formed through the first and second cover plates, respectively, and the sides of the opening formed through the flange of the hub during use. As a result, metal to metal contact therebetween is prevented, thus lowering the amount of noise that is generated during use of the torsional vibration dampening assembly.